You may wish to test the function of capacitor c9 10 uf 150 volt, and resistor r 68 within the control centre. Myself I believe it is the reversing switch. A simple test. Multi meter set on buzz/ohms. remove white 9 pin plug 4b
test between pin 7 and 3 operate the reversing lever a buzz or full scale reading should be obtained in one of its position. Now test between pin 7 and 4 again operate the reversing lever, a buzz or full scale reading should be obtained. The operating lever being the lever the carriage hits.
Ray Taylor, February 2010